The general aim of the present research plan is to determine the effect of pulsed electromagnetic fields (PEMF) on mid-palatal bone formation after rapid maxillary expansion (RME) in young cats. The specific aim of this investigation is to determine whether exposure to PEMFs after RME has an effect on the amount and rate of bone formed in the mid-palatal suture. The results obtained from these specific aims will determine whether the use of PEMFs will indeed increase the amount of bone formation in the mid-palatal suture after RME, thus decreasing the time of fixation required and ultimately the duration of active orthodontic treatment. It will also determine whether a study on clinical patients with maxillary constriction and/or cleft palate will be feasible. Twenty four male domestic cats at nine months of age will undergo RME of 5mm over 11 days. All animals will have this expansion secured. The animals will be divided into six groups of four each. Two groups will undergo PEMF application for 7 and 21 days respectively. Acrylic animal holders will keep the cats immobilized for the four hours of PEMF exposure each day. Two other groups will undergo similar immobilization for 7 and 21 days, but will not be exposed to PEMF. The final two groups, after RME, will remain unimmobilized for 7 and 21 days, respectively. At the end of the experimental period, the cats will be euthanized and the maxillae dissected. The tissues will be processed and studied histomorphometrically to analyze the rate and amount of bone formation at the widened inter-maxillary suture.